Case alumnus returns to teach SAGES class on human evolution

Robert Walter determined age of famous “Lucy” and
is now among geologists in search of modern human
origins

At first glance, a handful of dirt looks insignificant to first- and
second-year students in the Case Western Reserve University SAGES course “Geological
Evolution of Humans.” But Robert Walter, a visiting SAGES Presidential
Fellow and a Case alumnus, tells his class that sediment contains a
geological clock on human origins.

A world expert in geochronological techniques (the dating of rocks),
Walter has played an integral part in determining the age of early human
fossils, including several of the major finds of the past century. It
was the most famous of these finds—the partial skeleton of “Lucy,” a
human ancestor 3.2 million years old—that originally brought Walter
to Case as a graduate student in 1975.

Now a faculty member at Franklin and Marshall College in Lancaster,
Pa., Walter returned to Case this year to teach a special course for
the university’s new undergraduate initiative, the Seminar Approach
to General Education and Scholarship (SAGES). His course, which is similar
to ones he has taught for upper-level geology majors and graduate students,
examines human evolution in relation to the geological record.

“Sediments, not just fossil bones, answer key questions about
the age of hominids and the environments they lived in,” Walter
explained, “which enable us to understand the rates and nature
of evolutionary change”.

Along with geological and human history, Walter’s seminar explores
the history of science: He talked about how the evolution of our thinking
about evolution is as fascinating as the physical evolution of the species
itself. Class discussions and writing assignments focus on works by
scientists and theorists such as Charles Darwin, Charles Lyell, and
Donald Grayson. In addition, students will visit the Lucy exhibit at
the Cleveland Museum of Natural History—an exhibit about which
Walter is uniquely qualified to comment.

Pushing the Science

When Lucy was found in the Hadar region of Ethiopia in 1974, geologists
faced a dilemma. Radioactive carbon dating, the standard method at the
time, could date remains only as far back as 50,000 years. “Lucy
pushed the science,” Walter explained. To determine her age, scientists
would need another approach.

Walter, as an undergraduate at Franklin and Marshall in the early 1970s,
had studied volcanic rocks under the guidance of Stan Mertzman, who
had received his Ph.D. from Case just a few years before. Now, a member
of the team that discovered Lucy—James Aronson, a former Case
geologist currently at Dartmouth College—recruited Walter to apply
potassium-argon dating to the volcanic deposits that had surrounded
the remains. By dating the sediment above, around and below the find,
Walter and his colleagues could “bracket” Lucy’s age.

As geologists excavated additional fossils—some in valleys and
river beds contaminated with volcanic material from different eras and
areas—the dating methods had to become ever more precise. Walter,
as a post-doctoral fellow at the University of Toronto under Derek York,
helped developed new technologies, including laser-fusion, argon-argon
dating methods that have since been refined to the point where the age
of a volcanic particle as small as a grain of salt can be determined
with great precision and accuracy. When the age of each grain in a sample
is plotted on a graph, geologists can distinguish the contaminants from
the primary volcanic material (often a powdery, mineral-rich ash) and
determine the age of a fossil unearthed there.

Out of Africa

After receiving his doctorate from Case in 1981, Walter served as chief
geologist at the Institute of Human Origins, founded by Donald Johanson
who discovered Lucy while he was a member of the Case anthropology department.
For the past decade, Walter has done independent research in a region
of Eritrea (once northern Ethiopia), at the northern apex of what geologists
call the Afar Triangle. This geologically and tectonically active area
was the site for some of the last century’s most important hominid
finds.

Over millions of years, Walter explained, volcanic activity in the
Triangle caused the breaks and fissures of the Great Rift Valley, which
extends from Eritrea to Mozambique. In the process, human evolutionary
history was preserved in layers of sediment. Recent hominid discoveries
in this anciently populated region date back more than 5 million years,
making Lucy look like the baby of the fossil group.

Although Walter continues to work with hominid discoveries, he has
also branched off into a new and independent investigation, studying
early human migrations from Africa to other parts of the world. In a
1999-2000 field exploration of an area in Eritrea called the Danakil
Depression, Walter found stone tools and animal fossils along an ancient,
perched shoreline that he describes as “the bathtub ring of the
Red Sea.” These artifacts and fossils were deposited 125,000 years
ago, during the last interglacial period when sea levels were six meters
higher than they are today and when the climate was warmer and wetter.

This discovery, Walter said, provided “the earliest evidence
of human occupation of a coastal marine environment.” The geological
context of these tools suggest that early humans butchered large land
animals and harvested edible shell fish in what amounts to the earliest “surf
and turf” feast discovered so far. An adaptation to a seafood-rich
diet by 125,000 years ago marks an important, perhaps defining, shift
in early human behavior. This site also provides some of the first evidence
of where the migration of Homo sapiens out of Africa might have taken
place. Such coastal routes, it is now thought, allowed rapid expansion
of human populations throughout Eurasia and even Australia between 100,000
and 60,000 years ago.

Once he finishes teaching in SAGES, Walter plans to return to the area
and conduct excavations that will yield further information about this
ancient beach environment. Meanwhile, he has expanded his study of his
early finds to consider their implications for the history of evolution.
The connection between his research and the substance of his SAGES seminar
couldn’t be stronger.

“Even if the students never go into geology,” Walter said, “I
want them to have this fascination about early human origins, so that
when they read about a new discovery, they will have a deeper understanding
about their past.”

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